1. Technical Field
The present invention relates to capacitors and methods for manufacturing the same.
2. Related Art
The manufacturing technology relating to a variety of electronic devices having capacitors inside has evolved in recent years, and the application of those devices to computers, printers and other apparatuses is becoming more active. For example, memory devices formed with ferroelectric capacitors and piezoelectric devices formed with ferroelectric capacitors are highly expected as they are characterized by high-speed operation and low-power consumption.
Capacitors included in electronic devices generally have a structure in which a dielectric layer composed of an inorganic oxide sandwiched between two electrode layers composed of metal. With this structure, a charge may be accumulated, a structural change may be caused by polarization, or a displacement such as extension and contraction may be generated in the dielectric layer through the electrodes. The performance of such capacitors may be decided by the dielectric material, the electrodes, characteristics of their interface and the like. To improve the performance of the capacitors, the characteristic of each of the elements needs to be improved, and damage that may be inflicted on the capacitors during their manufacturing process need to be minimized.
Damage inflicted on capacitors during the manufacturing process may cause phenomenon, such as, an increased leakage current generated between the two electrodes, lowered reliability caused by deterioration of the interface, and the like. In particular, in the step of patterning the capacitors by dry etching, the leakage current may considerably increase because plasma directly acts on the dielectric material. Also, in devices in related art having capacitor structures, the capacitor structures may be covered by a barrier layer such as an aluminum oxide layer in order to improve their characteristics and prevent deterioration (see, for example, Japanese Laid-open Patent Application JP-A-2003-243625).
However, the use of an aluminum oxide film as a barrier layer for capacitors in piezoelectric devices may cause a problem in that displacement and contraction of the dielectric layers are restricted as the film of the barrier layer has a high Young's modulus.
According to the research made by the inventors, it has become clear that a leakage current is mainly generated through running along a side surface of the capacitor, in other words, along a side surface of the ferroelectric layer. It is believed that generation of composition change in the dielectric material caused by dry etching, destruction of the crystallinity of the dielectric material by collision of ions, injection of charges in the plasma into the dielectric material may be the causes of the increase in leakage current along the side surface of the ferroelectric material. Also, in the case of devices having the structure in which the capacitor is covered by a dielectric layer, such as, an aluminum oxide layer, a silicon oxide layer or the like, impurities contained in aluminum oxide or silicon oxide of the dielectric layer and hydrogen generated during the process of forming the dielectric layer reduce the inorganic oxide (dielectric material), which is believed to generate leakage current along the side surface of the ferroelectric layer.